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There are several interfaces available for searching the catalog for Chandra counterparts to sources of interest; they are listed below. However, if you have a long list of sources to cross-match against the CSC, it is recommended that you use the TOPCAT multiplie cone search feature, until a CSC cross-match service becomes available.

• CSCview, the main interface available for accessing catalog data (see also the command-line interface), has a cone search feature which allows you to search for CSC sources within a specified radial distance of an input celestial position. You can enter an R.A. and Dec. pair in Equatorial or Galactic coordinates into the provided fields, as well as a search radius in arcseconds, arcminutes, or degrees for a search on source position. If you have a long list of source positions to cross-match with the catalog, you can download the full list of CSC source positions from CSCview, and use any of a number of tools such as TOPCAT or Aladin to cross-reference the CSC source list with yours. Alternatively, you can try one of the methods listed below.

• The CSC limiting sensitivity on-line tool is available for accessing approximate sensitivity at specified celestial locations to help you determine CSC limits in identifying X-ray counterparts to sources of interest. The file upload feature of this tool allows you to input text files containing lists of R.A. and Dec. source positions, which is especially useful if you have a long list of sources to check. The approximate limiting sensitivity is given as photons cm^-2 s^-1 in the catalog's Broad (B) band of 0.5-7.0 keV. If no sensitivity value is returned for a given source position in the list, it is a good indication that the source is not included in Release 1 of the catalog (see the Caveats associated with this tool here.)

• Another (quick and fun) way to find out if your source is included in the catalog is via the CSC interface to Sky in Google Earth. This feature allows you to view the footprint of each Chandra observation on the sky, along with the CSC Release 1 footprint for comparison. After loading the CSC KML file into your My Places folder in Google Earth (instructions available here), simply enter a source name or position into the search field to locate your source on the sky, and then check to see if a CSC Release 1 field of view overlaps it. To learn the various reasons why your source might not be included in a particular release of the catalog, see FAQ #1 in the Sky Coverage section.

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